One existing method for detecting corrosion (disclosed in U.S. Pat. No. 6,805,788) employs electrochemical impedance spectroscopy. The conductivity of the monitored substrate is measured by locating a probe with a solid polymer electrolyte membrane that houses an electrode in contact with the surface of the substrate. Perturbations in an AC current or voltage across the monitored surface and the electrode are used to determine the impedance of the substrate. However, the probe monitors for differences—from one area of a monitored surface to another—in surface conductivity as an indication of corrosion activity, and requires access by the probe to the region of concern. Also, the probe appears unlikely to be sensitive to water ingress; instead it will only show actual corrosion.
WO 87/04525 discloses a corrosion sensor that compares the resistivity of a reference element (not exposed to corrosion) and that of a test element coating the reference element and exposed to corrosion. However, this approach relies on the relative resistivity of the reference and test elements, so always requires the use of the two elements.
WO 00/46593 discloses a micro-electronic bond degradation sensor with a sensor substrate having sensor circuitry and a sensor stud and a power stud extending therefrom. The sensor circuitry includes a voltage-to-current amplifier with an input coupled to the sensor stud and an output coupled to the power stud, and operable to convert a voltage signal occurring along the sensor stud to a current signal output along the power stud.